An intro to the physics of passive solar


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  • An intro to the physics of passive solar

    1. 1. An Intro to the Physics of Passive Solar Design GERREN D. SIMMS SHEPHERD UNIVERSITY
    2. 2. Presenters Gerren D. Simms  Brennen Pedigo Chemistry Department  Environmental Science Shepherd University Department  Shepherd University
    3. 3. Overview Historical Uses of Passive Solar Technology Orientation of the structure Thermal Mass Insulation Windows Overhangs and shading
    4. 4. Historical Uses of Passive Solar Technology
    5. 5. Pueblo ArchitecturePueblo architecture takesadvantage of thematerial, a mixture ofearth and straw. Adobe iswonderful thermal mass:it will store warmth in thewinter and it cools in thesummer. Copyright(C) 1999 David Slauson. This image is copyrighted. The copyright holder allows anyone to use it for any purpose, provided that the photographer is credited.
    6. 6. Taos Pueblo (continuously inhabited for over 1,000 years)Built between 1000 and 1450: Thick Adobe Wall Construction
    7. 7. Pueblos as Green Buildings Adobe provides a large thermal mass and it is a local green building product with healthy breathable walls They are built with materials on site Orientation: South-facing for passive solar gain Many adjacent units increases the energy efficiency—all have access to the south but the other directions are protected and “insulated”
    8. 8. Mesa Verde
    9. 9. Mesa Verde Great passive solar design principles in the Mesa Verde cliff dwellings. The southern orientation with the rock overhang means shade in the summer and solar gain in the winter. Furthermore, the rock and earth act as a thermal mass that stores the sun’s energy for use at night During the summer months, the thermal mass serves as a heat sink to help keep it cooler
    10. 10. Mesa VerdeStone covered with plaster
    11. 11. Assumptions at this point You plan on building a home North of the Equator
    12. 12. Terms for orientation of the structure Solar Azimuth (Ψ)- the angle of the sun from true south Solar Altitude (α)- the sun’s angle above the horizon Solar constant- How much sun we actually get on the building site  677 (W/m^2)
    13. 13. Orientation of the structure Orient the structure so that the maximum amount of sun can get in This includes having your house face true South that was calculated (using the solar azimuth and altitude) and using lots of windows to get the sun’s energy inside
    14. 14. Thermal Mass So, now we have the sun coming in for heat, let’s keep the heat we gained in the day until the sun comes up again tomorrow The structure’s southern side should have a large thermal mass so the sun coming into all the windows strike the thermal mass and that energy gets stored for the night
    15. 15. Direct Gain System In a direct gain system, large south facing windows are used to allow the sunlight in and a thermal storage material (concrete, slate, water, br ick, etc…) absorbs the solar radiation
    16. 16. Indirect Gain System An indirect gain system collects and stores the solar energy in one part of the structure and uses natural heat transfer to distribute this heat to the rest of the structure
    17. 17. Indirect Gain System Another example of indirect gain systems… Thermosiphoning
    18. 18. Math   Using the water as a thermal mass, how many Q mc T gallons would be necessary to store enough thermal energy for 3 days of space heating? Assume the water Q in the storage tank begins m c T at 150oF and has a useful lower limit of 90oF  You have already foundm 1440000Btu 25000lb 1gal 3012.05gal that you need 1,440,000 Btu 1.0 o 60oF 8.3lb Btu for 3 days lb F  Therefore m=25000 lbs~3000 gallons of water
    19. 19. Insulation So far, we have worked very hard to get all the sun’s energy that we can into the structure so lets keep it there The more insulation the better  BEST- Have the structure underground with an atrium providing the solar energy and light  BETTER- Have bermed walls on three sides of the structure  GOOD- Use Structured Insulated Panels (SIPs) when building the structure
    20. 20. Best- Underground This is the best type of structure for a passive solar structure because once the sun’s energy is inside, not much of it can get out The structure is surrounded on all sides by rammed earth (dirt), with only a Southern entrance or atrium exposed
    21. 21. Better- Berm it! A bermed structure is the second best option for passive solar design A bermed structure has earth around at least one wall to keep the energy inside the house
    22. 22. Good- SIPs Structured Insulated Panels (SIPs) are panels that can be used in place of “stick built” construction. They are attractive because they are highly insulated and easy to use, so construction labor costs goes down.
    23. 23. How do I figure out how much insulation I need?First you need to figure out which degree-day region you live in
    24. 24. What is a Degree-Day Here is an example of how a Degree-Day works:  March 18 had a high temp of 42oF and a low temp of 20oF 42 20 o F Mean Temp 31o F 2 Degree - Day(DD) 65 31 34 DD on March 18th
    25. 25. Ok, now what? Math  1 hourQtotal A 24 DD year R day 1 Btu 2 hQtotal 2 o 3000 ft 24 5000 DD 25,714 ,285 .71 14 ft h F dayQtotal 25 .7 10 6 Btu
    26. 26. Assumptions at this point You have decided to build a traditional style home using SIPs
    27. 27. Windows Lots of large windows that are at least double pane on the southern side of the home The Northern side of the home is where most of the cold and bad weather comes from so…  BEST- No windows on Northern side  BETTER- Few small windows on Northern side  GOOD- Plant quick growing evergreen trees about 6-10’ apart on the Northern side of the structure (This really should be done no matter what window choice is made)
    28. 28. Math Qc k A T Total heat transfer for 12 hours through an insulated t window that measures 4’x7’, when outside temp is 5oF and inside temp is 65oF? R value of window is 1.54R k 1Qc A T Qc t A T R t R 1Btu Qc 12h 28 ft2 (65 5)F 1.54 ft2 h  F Qc 13,100Btu
    29. 29. Overhangs and shading So now that we have the sun’s energy coming in and being stored and we also have the harsh elements out, let’s adjust it for the seasons using overhangs and shading. The proper use of overhangs and shading can allow all of the sun into the structure in the winter, but block it in the summer
    30. 30. Overhangs strategically placed
    31. 31. Using Vertical Glass
    32. 32. Plant Deciduous Trees on Southern Side Plant deciduous trees so they block the incoming sun in the summer, and once the leaves fall the winter sun can get through unobstructed
    33. 33. If you would like a copy of this you can… Go to our linkedin profiles for a link to this slideshow  